The spam campaign replaced direct links to the websites of Marriott, Hilton, Holiday Inn and many other hotels to the domains "roomstobook.info" or "roomstobook.net" on Google Plus listings.

As of Tuesday evening, those domains redirected to hotelswhiz.com, a booking site. It claims in its terms and conditions to be part of ian.com, which redirects to a website owned by travel giant Expedia explaining its affiliate marketing program, the Expedia Affiliate Network.

That program pays a commission to website operators who integrate Expedia's inventory of hotel listings into custom-built websites to sell more bookings.

Affiliate marketing programs and their participants often have to be vigilant against spammers, who sign up for the programs in attempts to make commissions from shifting traffic around.

Expedia could not be immediately reached despite a call and an email to its public relations company.